The exercise methods of waist muscles are: barbell sitting posture, flat support (waist and abdomen), prone from both ends, swimming standing, goat standing and so on. And many actions are improved versions of the above categories.
The exercise methods of back muscles are as follows: pull-ups, T-bar/barbell/one-arm dumbbell bending over and paddling, sitting down and so on.
You can find the specific action on the internet according to the name I said (it's easy to find). There's always one for you.
Besides, if you don't want to go to so much trouble, practice your back muscles. In fact, it is enough for you to master three movements. I strongly recommend it: barbell rowing, pull-ups and hard pulling. These three movements are the most important, classic and basic movements for practicing back in fitness circle. There is a lot of information on the internet, so I won't go into details. You can ask if you don't understand. Wish you success!